Research Demonstrates the Importance of Eggshell Cuticle Plugs

Dr. Maxwell Hincke, University of Ottawa, Ontario, Canada

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USPOULTRY and the USPOULTRY Foundation announced the completion of a funded research project at the University of Ottawa in Ontario, Canada, in which researchers demonstrated the importance of eggshell cuticle plugs. The research was made possible in part by an endowing Foundation gift from Midwest Poultry Services and is part of the Association’s comprehensive research program encompassing all phases of poultry and egg production and processing.

Dr. Maxwell Hincke and colleagues at the University of Ottawa recently completed a research project in which they studied the properties of the plug which fills the respiratory pores of eggshells. These plugs are very important for preventing the entry of harmful bacteria into the eggs. They found that these plugs remain intact following the commercial egg washing process in both white and brown eggs. The plugs appear to be chemically similar to the eggshell cuticle and likely contain antimicrobial proteins found in the cuticle. One of these proteins was successfully produced and purified, and its antimicrobial activity is being evaluated.

Project #F070: Genetic Modulation of the Antimicrobial Properties of the Egg Shell Cuticle Pore Plug

A pathogen-free egg is extremely important for the production of unfertilized eggs intended for human consumption. An intact eggshell cuticle, together with eggshell and eggshell membrane, is an effective physical and chemical barrier against bacterial contamination of the egg. In Canada and the United States, eggs are washed and graded before retail sale. This practice removes potential pathogens from the eggshell surface but also degrades the protective cuticle. Breeding programs have not focused extensively on cuticle quality and this study provides more insight into the role of eggshell cuticle in restricting bacterial access to egg interior via the respiratory pores.

The study demonstrated that the commercial washing process can abrade the outer surface cuticle; however, the pore plugs are still present to block bacteria from traversing the respiratory pores of the eggshell. A combination of analytical techniques was used to characterize the cuticle and pore plugs at the microscopic level. Scanning electron microscopy revealed that the plugs formed by the cuticle layer within the eggshell pores remain firmly lodged throughout the commercial washing process in both white and brown eggs regardless of hen age.

The chemical composition and quality of cuticle was also analysed. It appears that the cuticle and the pore plugs have a similar chemical composition which indicates that the pore plugs may be an extension of the cuticle. The antimicrobial proteins known to be present in the cuticle likely then also occur in the pore plugs. This study also revealed that cuticle composition and chemistry is influenced by hen age. In general, the amount of cuticle on eggs declined as hens aged, and the amount of protein in the cuticle also declined. This may indicate that the antimicrobial activity of the cuticle declines with hen age.

Ovacalyxin-32 (OCX-32) is one of the proteins found in the cuticle that is believed to have antibacterial properties. We successfully produced and purified OCX-32 in a system which used E.coli to produce the protein. Ongoing studies will characterize the antimicrobial properties of OCX-32 and determine whether it is playing a role in the antimicrobial function of the pore plug.

Our findings that pore plugs can withstand commercial washing will help to maintain consumer confidence in the important North American egg industry. This information will be beneficial for constructing strategies to evaluate and control the incidence of contamination in commercial eggs. Further studies are required to evaluate the localization of cuticle and pore plug antimicrobial proteins and their role in maintaining egg quality and preventing egg contamination.